Binding data from gridview checkbox

Question

Hi Friends,
I use 2 tables from database one is branch and subbranch
if i select branch all the subbranch should be selected and vice versa
finally all the values should be stored in database in another table



now my doubt is the items which are selected must be stored into a table named MAPTABLE it contains all the ID's of 3 table
mapid--> identity column
branchid--> checkbox
subranchid-->checkboxlist
how to stored the seleted checkbox items into my table.
THANKS IN ADVANCE